Digital television services and other multimedia service providers often desire to make some services selectively available to their customers. For example, a collection of channels might be made available only to customers who pay an extra monthly fee, or a video on demand movie may be available only to those who have paid the viewing fee. Conventional solutions for providing selectively available content rely on withholding encryption keys, or otherwise making it impossible for a client to decode an unauthorized part of the content stream. These types of conventional techniques succeed in enabling a degree of differential service, but a problem remains—deciding what to display in place of a denied video stream.
FIG. 1 shows a conventional multimedia system 100, in which a multimedia service provider offers content from a multimedia content store 102, via a headend 104. The headend 104 may transfer the multimedia content “as is,” or in some circumstances, the headend 104 may also include a conventional layer encryption engine 106 that sends the media content to clients as one or more encrypted versions or “layers.” At a first set top box 108, a conditional access module (CAM) 110 has access to a license or a decryption key for unlocking the multimedia content. Thus, at a monitor or television screen 112, the multimedia content is displayed. At a second set top box 114, however, the client's CAM 116 does not have access to proper credentials (license and/or decryption key) for unlocking the multimedia content. The conventional multimedia system 100 has no mechanism for providing a very flexible multimedia alternative for the denied content, so the monitor 118 is either left blank, the content is scrambled, or an “unavailable” message is displayed. Sometimes a mechanism for purchasing the denied content is provided with the “unavailable” message. What is needed in circumstances similar to this is a collection of presentation alternatives related to the denied content so that some of the alternatives can be presented on a channel in response to client conditions, such as the hardware and authorization reasons for the denial.